This paper will analyze five American Vietnam War movies in the context of Realism and Idealism. The term realism and idealism are mainly used in the field of history. Not only these terms used in diplomatic history but also vice and virtue dualism which are often used in American Foreign policy will be used in this paper. Creating a four quadrant diagram by placing a realism and idealism in horizontal axis and putting a vice and virtue in vertical axis will be the main part of this study. At the same time, in order to check the quality of this diagram, five Vietnam War movies are viewed. This is an experiment of mixing two essential concepts of American Diplomatic History. This study proves that introducing the theory of other discipline is useful to understand the historical background of war movies. In addition, categorizing the protagonist’s role in the movie and its transition will clearly reflect the trend of American society towards the war in America. Not knowing the background of American society will hinder the understanding of the movie, and at the same time, it will make it harder for students in the classroom to comprehend the true message intended in the movie. Utilizing this diagram in CLIL education will also enhance the understanding in the classroom.